We dereddened the photometry of each globular cluster using the reddening values given by [1]} together with the extinction coefficients from [2]}. We then transformed the subdwarf photometry,
from the Johnson-Cousins UBVRI system to the ACS/WFC filter system using eqn. 12 of [2]} together with the transformation coefficients given in Table 18 of their paper. We then fitted PARSEC isochrones [4]}
to the color-magnitude diagram of each cluster, and used the isochrone to select the cluster members. We then calculated the average color of the cluster stars as a function
of magnitude and define a main-sequence ridge line by cubic spline interpolation between the data points.
